RAID system having channel capacity unaffected by any single component failure

ABSTRACT

The RAID system of this invention is able to function with undiminished capacity despite the failure of any one DASD, connector, or storage array controller. A signal is produced when any component fails, thereby alerting the operator of the need to replace the failed component. The reliability of this RAID system is achieved by using two connectors for each connection, by using a spare DASD for each channel of DASD, and by providing a passive storage array controller able to assume the identify of and take over the control of the DASD controlled by a failed storage array controller. This is a reliable, inexpensive system for achieving unprecedented reliability in the storage and delivery of data.

CROSS-REFERENCE TO RELATED APPLICATIONS.

Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT.

Not Applicable

Reference to a “Microfiche appendix.”

Not Applicable

BACKGROUND OF THE INVENTION.

1. Field of the Invention

This invention relates to RAID systems with provisions for maintainingthe speed or channel capacity of the system under conditions of singlecomponent failure.

2. Description of Related Art Including Information Disclosed Under 37CFR 1.97 AND 37 CFR 1.98.

The present invention is a RAID system which has redundant connectionsbetween active storage array controllers and the arrays of storage unitsthey control, spare storage units in each array, and a passive storagearray controller which assumes the control of the array of storage unitsof any failed storage array controller. Thus the failure of any oneconnector, storage unit, or storage array controller does not affect thechannel capacity or speed of the RAID system of this invention.

U.S. Pat. No. 5,651,110 discloses a RAID system with two second levelstorage array controllers each of which control an array of disk drives.Each second level storage array controller is controlled by a separatefirst level storage array controller, which, in turn, communicates withthe computer. In the event of a failure of a second level storage arraycontroller, control of the array of disks assigned to the failed storagearray controller is assumed by the intact second level storage arraycontroller, which now controls both its original disks and the disks ofthe failed second level storage array controller. The channel capacityof the RAID system is thereby reduced by half under conditions of afailed second level storage array controller.

U.S. Pat. No. 5,787,070 discloses a global computer network packetswitching system in which a number of active service modules are backedup by a normally passive redundancy module which takes the load when oneof the active service modules fails. The communication system has noprovisions for data storage.

U.S. Pat. No. 5,790,775 discloses a data storage system with a SCSIenvironment. The system involves two storage array controllers indual-active, redundant configuration, and associated physical storagemedia. Failure of one storage array controller results in the otherstorage array controller assuming the control of all of the SCSI units(failover). The reverse operation, wherein the defective storage arraycontroller is repaired or replaced and assumes control of its portion ofthe storage media, is termed “failback”. The channel capacity of thedata storage system is reduced by half under conditions of a failedstorage array controller.

U.S. Pat. No. 5,848,230 discloses a RAID system in which there is triplereplication of all subsystems. It has three storage array controllers,one active and two which are normally passive and are used only in caseof the failure of the active storage array controller and (subsequently)the secondary storage array controller. In addition, triplicatesubsystems such as cooling and power subsystems are included. Thissystem provides highly reliable and continuous availability of storageservice and an undiminished channel capacity. The provision of twonormally passive storage array controllers for each active storage arraycontroller is a major contributor to the cost of this system.

U.S. Pat. No. 5,872,906 discloses a RAID system with provisions forallocating a spare disk unit in case of a disk failure. It includes twosubstorage array controllers which are provided for the common busesthereby distributing the processing functions of the storage arraycontrollers and reducing a load. No provisions for failure of a storagearray controller are disclosed.

U.S. Pat. No. 5,922,077 discloses a RAID system with two storage arraycontrollers and a fail-over switch which routes the data from thestorage array controller of a failed communication path to the operatingstorage array controller, which then handles the load of both storagearray controllers. The channel capacity is reduced when one storagearray controller is handling both loads.

U.S. Pat. No. 5,944,838 discloses a RAID system with a redundant storagecontrol module (RDAC) in which two queues of pending I/O requests aremaintained for a single array of storage devices. The redundant queuetakes over on the failure of the active queue. The redundant queuecopies each I/O request sent to the active path which minimizes the timerequired for the redundant queue to take over the functions of theactive queue.

U.S. Pat. No. 6,073,218 discloses an apparatus for coordinating multipleRAID storage array controllers' access to a single array of storagedevices. Each of a number of storage array controllers process differentI/O requests on an array of common shared storage devices. One storagearray controller is designated primary with respect to the storagedevices. Concurrent access to the storage devices is coordinated by thestorage array controllers.

None of the prior art RAID systems achieves the advantages of thepresent invention, that of preserving the channel capacity or speed ofthe system in the face of failure of a connector, storage unit, orstorage array storage array controller, all with minimal redundancy ofcomponents and minimal cost. In particular, in this invention a singlepassive storage array controller is available to replace any one of twoor more active storage array controllers when an active storage arraycontroller becomes defective.

BRIEF SUMMARY OF THE INVENTION

This invention is RAID system which is able to function withundiminished channel capacity or speed despite the failure of any onecomponent, with minimal redundancy of components. The system comprises nactive storage array controllers, n arrays of storage units, each activestorage array controller controlling one or more arrays of storageunits, and one only passive storage array controller. The passivestorage array controller is connected by two connectors to each activestorage array controller, and is able to control any one of the arraysof storage devices. In the event of failure of any of the active storagearray controllers, the passive storage array controller assumes theidentity of the failed storage array controller and assumes control ofthe array of storage devices of the failed storage array controller.Since each array of storage units contains a spare unit which becomesactive when one storage unit in the array fails, the RAID system of thisinvention is able to function with undiminished capacity in the event offailure of any one storage unit or any one storage array controller. Inanother embodiment, each storage unit is connected to controllers by twoconnectors, and this embodiment is, in addition, able to function in theevent of failure of any one connector.

The objective of this invention is to provide a RAID system withundiminished capacity despite the failure of any one storage unit, anyone connector, or any one storage array controller.

Another objective is to provide a RAID system which produces a signalfor the operator in the event of failure of any component.

Another objective is to provide a RAID system which automaticallysubstitutes a replacement for a failed storage unit or storage arraycontroller.

Another objective is to provide a RAID system with redundant connectorsconnecting the storage units and the storage array controllers.

Another objective is to provide a RAID system with several activestorage array controllers which normally control the arrays of storageunits and with one passive storage array controller which assumescontrol the storage units of any active storage array controller whichfails.

Another objective is to provide a RAID system capable of functioningwith undiminished channel capacity in the event of failure of aconnector, storage unit, or storage array controller with minimalredundancy of components.

Another objective is to provide a RAID system capable of functioningwith undiminished channel capacity in the event of failure of aconnector, storage unit, or storage array controller without incurringthe expense of a back-up storage array controller for each activestorage array controller.

Another objective is to provide a RAID system capable of functioningwith undiminished channel capacity in the event of failure of aconnector, storage unit, or storage array controller at minimal expense.

A final objective is to produce a RAID system simply constructed ofinexpensive, readily obtainable components without adverse effects onthe environment.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS.

FIG. 1 is a diagrammatic depiction of a single RAID subsystem.

FIG. 2 is a diagrammatic depiction of a redundant single RAID subsystem.

FIG. 3 is a diagrammatic depiction of the first embodiment RAID systemof this invention having three active storage array controllers and onepassive storage array controller.

FIG. 4 is a diagrammatic depiction of the second embodiment RAID systemof this invention having three active storage array controllers and onepassive storage array controller.

FIG. 5 is a diagrammatic depiction of the third embodiment RAID systemof this invention having n active storage array controllers and onepassive storage array controller.

FIG. 6 is a diagrammatic depiction of the fourth embodiment RAID systemof this invention having n active storage array controllers and onepassive storage array controller.

FIG. 7 is a diagrammatic depiction of the fifth embodiment RAID systemof this invention having two active storage array controllers and onepassive storage array controller.

FIG. 8 is a flow chart showing the process of detecting the failure ofan active storage array controller by an adjacent storage arraycontroller, assuming the duties of the failed active storage arraycontroller by the passive storage array controller, and signaling theoccurrence of a failure.

FIG. 9 is a flow chart showing the process of detecting the failure ofan active storage array controller by the passive storage arraycontroller, assuming the duties of the failed active storage arraycontroller by the passive storage array controller, and signaling theoccurrence of a failure

DETAILED DESCRIPTION OF THE INVENTION.

In this patent application the term “channel capacity” means the abilityof a given channel subject to specific constraints to transmit messagesfrom a specified message source expressed as the maximum possibleaverage transinformation rate, which can be achieved with an arbitrarysmall probability of errors by use of an appropriate code. The channelcapacity of a RAID system is commonly referred to as the “speed” of thesystem.

FIG. 1 is a schematic of the external view of a RAID system referred toin this application as a “single RAID subsystem” 11. The single RAIDsubsystem comprises a storage array controller 30, and an array ofdirect access storage devices (DASD) or storage units 40-61. A hostcomputer is electrically connected to the storage array controller 30 byconnector 20.

Any suitable connector may be used, such as a wire, copper wire, cable,optical fiber, or a SCSI bus.

In all of the Figs. the convention is followed of depicting connectorswhich are not electrically connected as lines which crossperpendicularly. An electrical connection is indicated by a line whichterminates perpendicularly at another line or at a symbol for acomponent. Thus in FIG. 1 a host computer (not shown in FIG. 1) iselectrically connected to storage array controller 30 by connector 20.The host computer is not considered part of the single RAID subsystemand is not shown in FIG. 1. Connector 401 is electrically connected tostorage array controller 30 and to DASD 1A 40 and to DASD 1B 41, but isnot electrically connected to connectors 402 to 406. Connector 402connects storage array controller 30 with DASD 2A 42 and DASD 2B 43.Connector 403 connects storage array controller 30 with DASD 3A 44 andDASD 3B 45. Connector 404 connects storage array controller 30 with DASD4A 46 and DASD 4B 47. Connector 405 connects storage array controller 30with DASD 5A 50 and DASD 5B 51. Connector 406 connects storage arraycontroller 30 with DASD 6A 60 and DASD 6B 61.

In the configuration in FIG. 1, for example, data are striped over DASD1A 40, DASD 2A 42, DASD 3A 44, and DASD 4A 46. DASD 5A 50 is a paritydisk which is used to check the accuracy of data striped on the disksDASD 1A-4A and to substitute for a failed DASD. DASD 6A is a spare diskwhich is used to substitute for any one of disks DASD 1A-5A which havefailed.

DASD may be disks, tapes, CDS, or other suitable storage device. Apreferred DASD is a disk.

All the storage units or DASD and connectors in a system taken as awhole is referred to as an “array” of storage units or DASD,respectively. In the examples here the DASD are arranged in channelswhich consist of a number of DASD which are electrically connected toeach other and to the storage array controller by connectors. Thechannels are designated in FIG. 1 as 1-6. The number of channels mayvary. A preferred number of channels is 6.

A channel, for example channel 1, consists of connector 401, DASD 1A 40,and DASD 1B 41. Although only two DASD are depicted in channel 1 of FIG.1, there may be as many as 126 DASD in a channel. A preferred number ofDASD in a channel is five.

A group of DASDs served by separate channels across which data isstriped is referred to as a “tier” of DASDs. A DASD may be uniquelyidentified by a channel number and a tier letter, for example DASD 1A isthe first disk connected to channel 1 and tier A of the storage arraycontroller.

A preferred storage array controller is the Fibre Sabre 2100 FibreChannel RAID storage array controller manufactured by Digi-DataCorporation, Jessup, Md.

Additional tiers of DASDs may be used.

Any suitable host computer may be used. A preferred host computer is aPENTIUM microchip-based personal computer available from multiplevendors such as IBM, Research Triangle park, North Carolina; CompaqComputer Corp., Houston Tex.; or Dell Computer, Austin, Tex. PENTIUM isa trademark for microchips manufactured by Intel Corporation, Austin,Tex.

FIG. 2 is a schematic of a RAID system referred to in this applicationas a “redundant single RAID subsystem” 21. The redundant single RAIDsubsystem 21 is identical to the single RAID subsystem 11 of FIG. 1except that each DASD in the redundant single RAID subsystem isconnected to the storage array controller 30 by two connectors.Connector 501 is connected to disk array storage array controller 30 andto DASD 1A 40 and DASD 1B 41. Connector 502 connects storage arraycontroller 30 with DASD 2A 42 and DASD 2B 43. Connector 503 connectsstorage array controller 30 with DASD 3A 44 and DASD 3B 45. Connector504 connects storage array controller 30 with DASD 4A 46 and DASD 4B 47.Connector 505 connects storage array controller 30 with DASD 5A 50 andDASD 5B 51. Connector 506 connects storage array controller 30 with DASD6A 60 and DASD 6B 61.

The single RAID subsystem 11 in FIG. 1, and redundant single RAIDsubsystem 21 in FIG. 2 therefore are protected against failure of anytwo disks, by the inclusion of a parity disk DASD 5A 50 and DASD 5B 51and by the inclusion of a spare disk DASD 6A 60 and DASD 6B 61 in eachchannel. The redundant single RAID subsystem 21 in FIG. 2 is protectedagainst failure of any single connector which connects a DASD to thestorage array controller 30 by the inclusion of two connectors, forexample 401 and 501, which connect each DASD, for example DASD 1A 40, tothe storage array controller 30.

FIG. 3 shows the first embodiment RAID system of the present invention.In this system, the storage array controller of redundant RAID subsystem21 is connected to the storage array controller of redundant RAIDsubsystem 121 by two connectors, depicted in FIG. 3 as connectors 114and 116. All connectors in FIG. 3 are bidirectional connectors.Subsystem 121 is connected to subsystem 221 by connectors 118 and 120.Subsystem 221 is connected to subsystem 21 by connectors 122 and 124.Subsystems 21, 121, and 221 each has an array of DASD and are used fornormal RAID functions. Each storage array controller of subsystems 21,121, and 221 therefore is attached to two adjacent storage arraycontrollers, forming a ring of storage array controllers. The storagearray controllers for subsystems 21, 121, and 221 are referred to as“active” storage array controllers because in the normal function of theRAID system these storage array controllers are actively involved incontrolling the arrays of DASD in reading and writing data.

Storage array controller 100 is similar to the storage array controllersof subsystems 21, 121, and 221 except that it is not normally associatedwith an array of DASD. Storage array controller 100 is a “passive”storage array controller and serves as a back-up for the storage arraycontrollers associated with subsystems 21, 121, and 221. Storage arraycontroller 100 is connected to the storage array controller of subsystem21 by connectors 102 and 104; to the storage array controller ofsubsystem 121 by connectors 110 and 112; and to the storage arraycontroller of subsystem 221 by connectors 106 and 108.

The storage array controller of subsystems 21, 121, and 221 containinternal software which generates a binary signal termed a “normaloperating signal” or a “heartbeat” at an interval of a few millisecondswhen the storage array controllers of the respective subsystems areoperational. When the storage array controller is in a defectivecondition, the emission of the normal operating signal ceases.

The normal operating signal is emitted from the storage array controllerof subsystem 21 over connector 114 to the disk array storage arraycontroller of subsystem 121. In similar fashion, the normal operatingsignal is emitted from the storage array controller of subsystem 121over connector 118 to the storage array controller of subsystem 221.Finally, the normal operating signal is emitted from the storage arraycontroller of subsystem 221 over connector 122 to the storage arraycontroller of subsystem 21.

When one storage array controller, for example 121, no longer receivesthe normal operating signal because the storage array controller of theadjacent subsystem, 21 in this example, is defective, the receivingstorage array controller 121, referred to as the “reporter” storagearray controller, emits an activation signal to the passive storagearray controller 100. On receipt of this activation signal, the passivestorage array controller 100 assumes the identify of the failed storagearray controller of subsystem 21. The passive storage array controllerconsults a table stored on each DASD and identifies the DASD of thedefective storage array controller 21. The passive storage arraycontroller 100 then assumes control of the DASD array of subsystem 21.

In the first embodiment depicted in FIG. 3 each active controller 21,121, and 221 also emits a heartbeat to the passive controller 100 overconnectors 102, 110, and 106, respectively. Failure of the heartbeatfrom any one active controller also activates the passive controller toassume identify of the failed controller, as described above. Thissystem provides redundancy in that the passive controller is signaledconcerning the failure of an active controller by both indirectly by thereporter storage array controller and directly by the failure of theheartbeat from the defective active storage controller.

Finally, failure of an active storage array controller 21 causes thereporting storage array controller 121 or the passive storage arraycontroller 100 to emit a warning signal which indicates to the operatorof the RAID system that a storage array controller has failed andrequires repair or replacement.

Although a single connector is described in the above example, each diskarray storage array controller may be connected to adjacent storagearray controllers by two redundant connectors. This assures that thefailure of one connector between storage array controllers will notresult in the loss of communication between the storage arraycontrollers, because the other connector will convey the signal. In asimilar fashion, the passive storage array controller 100 may beconnected to the storage array controllers of subsystems 21, 121, and221 by two redundant connectors which assure communications in the eventof failure of any one connector. Thus the passive storage arraycontroller is able to assume the identity and function of any of theactive storage array controllers even in the event of the failure of anyone connector between the passive storage array controllers and theactive storage array controllers.

FIG. 4 shows a second embodiment of the RAID system of the presentinvention. The second embodiment shown in FIG. 4 is the same as thefirst embodiment shown in FIG. 3 except that the connectors 114-124 areomitted. The second embodiment has the advantage of lesser costs, ascompared to the first embodiment, but, on the other hand, the secondembodiment lacks the redundance afforded by the first embodiment.

FIG. 5 depicts a third embodiment RAID system with n redundant singleRAID subsystems. The system of FIG. 5 is the same as that of FIG. 3except for the inclusion of additional redundant single RAID subsystemsrepresented by redundant single RAID subsystems n−1 and n. In theembodiment of FIG. 5, the connections between redundant single RAIDsubsystems 21, 121, and 221 with passive storage array controller 100are as in FIG. 3 with the exceptions that subsystem 121 is connected tosubsystem n−1 by connectors 130 and 132, and subsystem 221 is connectedto subsystem n by connectors 146 and 148. Subsystem n−1 is connected tosubsystem n by connectors 138 and 140. Passive storage array controller100 is connected to subsystem n−1 by connectors 134 and 136. Passivestorage array controller 100 is connected to subsystem n by connectors142 and 144.

FIG. 6 shows a fourth embodiment of the RAID system of the presentinvention. The fourth embodiment shown in FIG. 6 is the same as thethird embodiment shown in FIG. 5 except that the connectors 114, 116,122, 124, 130, 132, 138, 140, 146, 148, are omitted. The fourthembodiment has the advantage of lesser costs, as compared to the thirdembodiment, but, on the other hand, the fourth embodiment lacks theredundance afforded by the third embodiment.

In the first to fourth embodiments of the RAID system described aboveand shown in FIGS. 3-6, a component of each embodiment is the redundantsingle RAID subsystem, 21 in FIG. 2. The single RAID subsystem, 11 inFIG. 1, may be substituted for the redundant single RAID subsystem inthe first to fourth embodiments. It should be noted that the failure ofthe single connector which connects the DASD of an array in a singleRAID subsystem, 11 in FIG. 1, as incorporated in embodiments two to fourof the RAID system, does not affect the channel capacity of the RAIDsystems of this invention. Failure of the single connector in a singleRAID subsystem, 11 in FIG. 1, does affect the ability to access andstore data in the DASD of the array. The loss of data access on thefailure of a single connector is avoided in the redundant single RAIDsubsystem, 21 in FIG. 2, which has two connectors between each DASD andstorage array controller.

FIG. 7 shows a fifth embodiment of the RAID system of the presentinvention. In FIG. 7, there are two active storage array controllers,620 and 640, and one passive storage array controller 600. Activestorage array controller 620 is connected to passive storage arraycontroller 600 by connectors 606 and 608. Active storage arraycontroller 640 is connected to passive storage array controller 600 byconnectors 607 and 609.

Active storage array controller 620 has in its first channel dual-portedDASD 621-625 and is connected to these DASD by connector 631. Activestorage array controller 620 has in its second channel dual-ported DASD626-630 and is connected to these DASD by connector 632.

Active storage array controller 640 has in its first channel dual-portedDASD 646-650 and is connected to these DASD by connector 641. Activestorage array controller 640 has in its second channel dual-ported DASD651-655 and is connected to these DASD by connector 642.

Connector 631 is also connected to the dual-ported DASD 646-650.Connector 632 is also connected to the dual-ported DASD 651-655.

Connector 641 is also connected to the dual-ported DASD 621-625.Connector 642 is also connected to the dual-ported DASD 626-630.

Passive storage array controller 600 is connected by connector 602 toconnector 631 and by connector 604 to connector 632.

In the fifth embodiment RAID system, therefore, each of the two activestorage array controllers, 620 and 640, and the passive storage arraycontroller 600, are connected to each of the DASD. Each DASD has twoconnectors leading directly or indirectly to the active and passivecontrollers. Failure of either of the active controllers or one of theconnectors leading to the DASD will result in the assumption of controlof the DASD involved by the passive storage array controller.

FIG. 8 is a diagram of the process which occurs after failure of astorage array controller described above with reference to the firstembodiment depicted in FIG. 3. The failure of the defective storagearray controller 121 of a redundant single RAID subsystem halts theemission of the heartbeat in step 510. The adjacent storage arraycontroller 221, termed the “reporter” storage array controller, notesthe cessation of the heartbeat emitted by the defective storage arraycontroller and emits an activation signal 520. Using its associatedinterface chip, the passive storage array controller 100 assumes theidentity of the defective storage array controller 121 in step 530. Thepassive storage array controller 100 also identifies the DASD of thedefective storage array by reading a table of DASD addresses and storagearray controller assignments previously stored on each DASD 540. Thenewly activated passive storage array controller 100 assumes control ofthe DASD of the defective storage array controller 121 in step 550.Finally, the reporter storage array controller 221 or the newlyactivated passive storage array controller 100 emits a warning signal toalert the operator of the RAID system to the need for repair orreplacement of the defective storage array controller in step 560.

FIG. 9 is a diagram of an alternate process which occurs after failureof a storage array controller described above with reference to thefirst embodiment depicted in FIG. 3. The process is the same as in FIG.8 except that step 520 is deleted and in step 580 the passive storagearray controller 100 detects the cessation of the heart beat. In allother respects the process in FIG. 9 is identical to that in FIG. 8.

Although the above example depicts a RAID system having three redundantsingle RAID subsystem and one passive storage array controller, thenumber of redundant single RAID subsystems may range from 1 to n, wheren is a arbitrary number, as in FIGS. 5 and 6. A preferred range for n is2-20. Of course, the larger n is, the lower the relative additional costof including the passive storage array controller in the system. On theother hand, the larger n is, the greater is the chance, however remote,that greater than one storage array controller will fail before thefirst failed storage array controller is repaired or replaced by theoperator.

The RAID system of this invention is characterized by undiminishedchannel capacity despite failure of a DASD, connector, or storage arraycontroller. Thus the channel capacity (C) of a RAID system comprised ofn single RAID subsystems, or n redundant single RAID subsystems, each ofwhich has the same capacity c, is C=(n)(c) despite the failure of anyone of a DASD, connector or storage array controller. This is animportant advantage over conventional RAID systems because theconventional RAID systems suffer diminished capacity when a connector,or storage array controller fails. In particular, if a conventional RAIDsystem comprises two subsystems and operates without a failed componentat a capacity C=2(c) and one storage array controller or connectorfails, the capacity of the RAID system becomes C=c. Thus in this examplethe capacity is reduced by half by the failure of a connector or storagearray controller.

In the more general case, if a conventional RAID system comprises nsubsystems, the capacity of the normally operating system is C=(n)(c),and the capacity after the failure of a subsystem is C=(n−1)(c). Thusthe capacity is reduced by a factor related to the number of subunits bythe failure of a subsystem.

It will be apparent to those skilled in the art that the examples andembodiments described herein are by way of illustration and not oflimitation, and that other examples may be used without departing fromthe spirit and scope of the present invention, as set forth in theappended claims.

We claim:
 1. The process of maintaining the channel capacity of a RAIDsystem having storage array controllers which control direct accessstorage devices (DASD) and which generate a binary signal termed aheartbeat when the storage array controllers are operational when anactive storage array controller fails comprising the steps of: a.ceasing the emission of the heartbeat by a defective active storagearray controller, b. detecting the cessation of the heartbeat by adefective active storage array controller and emission of an activationsignal by a reporter active storage array controller, c. detecting theactivation signal by a passive storage array controller and assuming theidentity of the defective active storage array controller by the passivestorage array controller, d. identifying the DASD of the defectivestorage array controller by the passive storage controller using a tableon each DASD, e. assuming control of the DASD of the defective storagearray controller by the passive storage controller.
 2. The method ofclaim 1 further comprising after step e: f. emitting a defective storagearray controller signal by the reporter storage array controller or thepassive storage array controller.